Magnitude

Measure of the energy released in an earthquake, obtained from interpretation of seismograms. For technical reasons several different magnitude scales are in common use. At PNSN we use the following: Md (Duration Magnitude) - based on the duration of shaking. Ml (Local Magnitude) - based on the peak amplitudes of high frequency seismograms, and Mw (Moment Magnitude) - based on matching waveforms of the lowest frequency ground motions in broad-band seismograms. More information at: http://earthquake.usgs.gov/earthquakes/glossary.php#magnitude and http://neic.usgs.gov/neis/phase_data/mag_formulas.html

(Origin) Time

Date and Time when the earthquake rupture initiated. Large earthquake ruptures can take many seconds to finish. Seismologists usually use Grennwich Mean Time (GMT) to avoid confusion ariasing from mixing observations from different time zones. However, the local time is also given as a reference for what local residents experience.

Coordinates

Location in geographic coordinates (as Latitude, Longitude in decimal degrees) of the position on Earth's surface directly above where an earthquake rupture initiated. PNSN coordinates are referenced to the WGS84 ellipsoid.

Depth

Depth within the Earth where an earthquake rupture initiated. PNSN reports depths relative to sea level, so the elevation of the ground above sea level at the location of the epicenter must be added to estimate the depth beneath the Earth's surface.

Number of Phases

Number of P and S arrival-time observations used to compute the hypocenter location. In general, more arrival-time observations result in improved earthquake locations.

RMS Misfit

How well the given earthquake location predicts the observed phase arrivals (in seconds). Smaller misfits mean more precise locations. The best locations have RMS Misfits smaller than 0.1 seconds.

Azimuthal Gap

A measure of how well network seismic stations surround the earthquake. Measured from the epicenter (in degrees), the largest azimuthal gap between azimuthally adjacent stations. The smaller this number, the more reliable the calculated horizontal position of the earthquake.